Elongated particles, such as chips or fibres, are used in the manufacture of structural products, e.g. boards made of wood material, especially OSB boards (oriented strand board). OSB boards are fabricated from relatively large chips of different lengths, which are scattered in suitable orientations onto a base together with a binding agent and pressed to produce boards. Short chips should mainly be used in the middle layer of the board, while longer chips should be used in the surface layers. This is advantageous in respect of the board properties, e.g. bending strength. The chips in the surface layers are usually oriented in the longitudinal direction, i.e. in the direction of the longer side of the finished product, while the chips in the middle layer are oriented in the transverse direction or they are not given any particular orientation at all. In prior-art procedures for the production of OSB and waferboards, very short chips, obtained e.g. from a chip cutting machine, are screened out from the process because they have caused deterioration of the dimensional stability and strength properties of the end product as well as a high consumption of binding agent. Typically, about 15% of the chips used as raw material are screened out because they are too short to be included in the product. Prior-art scattering/orienting apparatus are not able to fractionate and/or orient the material being scattered well enough to allow very short particles to be utilised in board manufacture. If admitted into the process, very short chips would impair the board quality because they cannot be scattered on the desired part of the board or oriented accurately enough.
The object of the present invention is to achieve a completely new type of procedure and apparatus as well as a product which make it possible to avoid the existing drawbacks of prior art and thus to utilise even very short particles in the fabrication of structural products, such as boards.
The procedure and apparatus of the invention have numerous significant advantages. The material to be scattered may contain even relatively short particles and they can be scattered on a desired part of the board and, if necessary, oriented. This allows e.g. the raw material to be more fully utilised. Using the apparatus of the invention, the material can be fractionated better than before and therefore better scattering and orienting results are achieved. These circumstances signify that the quality of the final product is also improved. Thus, in the structural product blank of the invention, smaller particles can be used than at present without impairing the strength or rigidity of the product or its stability against deformation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.